Eight bacterial species account for 65% of all blood culture isolates, although this varies with patient population. Typically these are Escherichia coli (˜20%), Staphylococcus aureus (˜20%), Pseudomonas aeruginosa (7%), Enterococcus spp. (5%), Klebsiella spp. (˜5%), Enterobacter spp. (˜4%), Proteus spp, and Pneumococci (˜3%). In addition coagulase negative Staphylococci are frequently isolated from patients with intra-vascular devices but many of these isolates are clinically insignificant. The remaining 35% of blood culture isolates comprise upwards of 50 different species. Rapid detection of these numerous species with a single test would be very useful.
In recent years much effort has been invested in the production of species specific primers which can be used to identify an organism in a simple PCR reaction. If a PCR product of the expected size is produced with a set of these primers the presence of the target bacterium can be predicted with almost total certainty. Unfortunately this approach is not ideal for analyzing samples which may contain one of many pathogens. Analysis of such specimens using this approach requires a multiplex PCR containing a complex mixture of primers, a series of individual PCR reactions run in parallel to detect each species which may be present, or a series of PCR reactions run sequentially. Because of the potentially large number of different bacterial species that may be isolated from blood, these methods are unsatisfactory for the routine screening of general microbiological specimens.